1. Field of the Invention
The present invention relates to a method for manufacturing an active matrix array substrate and to a method for manufacturing a liquid crystal display using the same, more particularly relates to a method enabling efficient detection of pixel faults during the manufacturing process.
2. Description of the Related Art
Liquid crystal displays (LCDs) may be roughly divided into several types depending on their method of drive. One of the driving methods of an LCD is the active matrix system. In this type of LCD, a switching element and, if necessary, a capacitor element are provided and connected for each pixel at the matrix intersections of gate lines and data lines so as to improve the contrast, response, and other facets of display performance.
The LCD of active matrix system has an active matrix array substrate, on the surface of which substrate are arranged, in a matrix, pixel drive cells each comprised of a switching element for selecting a pixel and a capacitor connected to the switching element in series. Each pixel drive cell is provided with a pixel electrode corresponding to a pixel.
On this active matrix array substrate, a counter substrate is arranged substantially in parallel a predetermined distance away. The counter substrate is comprised, for example, of a glass substrate. On the surface of the counter substrate facing the active matrix array substrate (drive substrate) is laid a transparent counter electrode. Between the counter substrate and the drive substrate a liquid crystal is filled so as to form the liquid crystal layer.
To manufacture such an LCD, the drive substrate and the counter substrate on which the counter electrode is formed as a film are produced separately, assembled together substantially in parallel with a predetermined distance between them, and the space between them in filled with a liquid crystal, whereby a sealed liquid crystal layer is formed.
Not all the LCDs formed in this way, however, will be good ones free of pixel faults, so it is necessary inspect each LCD to determine if it has any pixel faults. The method used to inspect active matrix type LCDs for pixel faults after the liquid crystal is filled is to actually drive the LCD and analyze the image by an image processing device to inspect for faults or to inspect for faults visually. As a method used to inspect active matrix type LCDs for pixel faults after the liquid crystal is filled, there is the method disclosed in Japanese Unexamined Published Patent Application (Kokai) No. 63-123093, for example.
In this method, however, an image is actually displayed on the LCD for the inspection, so the inspection takes a long time and therefore productivity suffers. Further, since this inspection of pixel faults was performed on the LCDs after they were filled with liquid crystal, there was the problem that when a pixel fault was discovered, the LCD having that fault had to be discarded. This is because it is not practical in terms of manufacturing costs etc. to drain the liquid crystal from an LCD once it has been filled, repair the faulty portion or replace the faulty drive substrate, then refill the liquid crystal.
Therefore, a method has been proposed for inspecting for pixels faults of an LCD before the liquid crystal is filled.
The main means for inspecting for pixel faults of an LCD before filling with a liquid crystal are as follows:
First, the method is known of placing direct contact pins on the X and Y rows on the surface of the active matrix array substrate and performing a direct current (DC) test of the drive cells corresponding to the pixels.
In this technique, the DC test is repeatedly performed in the X and Y directions to detect faults in all the pixels. This method has the defects that it requires the same number of direct contact pins as the X, Y pixels and that the time required for the test is long (about one to five minutes). In particular, this technique cannot be used for LCDs including H/V scanners (horizontal and vertical scanning circuits) where the X and Y terminals do not stick out.
Second, there is the method of using a special crystal to detect the pixel faults as the light intensity (one to two minutes required for measurement).
In this method, instead of a liquid crystal, a special sheet-like crystal which changes in index of refraction in accordance with the voltage applied to it is placed on the surface of the active matrix array substrate. Laser light is input on the crystal and the light passing through it or reflected from it is detected so as to catch faults in the pixels. In this method, information detected as light has to be processed again by a camera, so the processing becomes complicated. Further, it is not possible to perform the test in the actual driving state. In addition, there is the problem that the resolution becomes insufficient and detection is not possible if the size of the pixels is less than several tens of microns.
As a third method, there is the method inspecting the LCDs before filling with liquid crystal from above by a camera or linear sensor (three to five minutes required for measurement).
In this method, however, while it is possible to detect physical faults of the pixels, it is not possible to detect electrical faults.